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Most younger patients who undergo head-region CT exams aren’t exposed to enough radiation to put them in danger of developing cataracts, according to a recent analysis published in Clinical Radiology.

Head exams are the most common CT examination among young people, wrote R.W. Harbron, with Newcastle University in the U.K., and colleagues. The eye is typically included when using infraorbital-metal baseline (IMB) techniques and may also be included during supraorbital-meatal baseline (SMB) positioning.

Exposing the lens of the eye to radiation results in the formation of cataracts, the researchers wrote. However, they went on to say that “it’s unclear if the risk of cataract induction is, or ever has been, sufficiently high to influence examination technique.”

Harbron and colleagues analyzed more than 448,000 head-region CT exams from 284,878 children and young adults performed in the UK between 1985 and 2014.

Most patients (72%) underwent a single head-region exam; a small number (roughly 1%) of patients received 10 scans or more and 0.1% underwent 20 CTs or more. In total, the lens was included in 57% of head exams.

When the eye was fully included, radiation dosages to the lens were 20–75 mGy (mean of 47 mGy), and when fully excluded that dose dropped to 2-7 mGy (mean of 3.1 mGy). More than 2,300 patients had a potential cumulative lens dose of more than 500 mGy.

“The findings from the present study suggest that the risk of cataract induction is likely to be small for the majority of young people undergoing CT examinations of the head,” the group wrote. “Although single examination doses are unlikely to induce cataracts…hundreds, perhaps thousands, of children and young adults have reached cumulative lens doses of several hundred milligray by having undergone multiple head examinations using older-generation equipment, with the eyes included within the primary irradiated field.”

This does not mean, the researchers explained, that CT imaging has caused thousands of cataracts, but should encourage more discussion and research into the threshold dose for cataract induction.

And while there are clinical advantages to including the eye in CT head exams, the patient’s best interest must come above all else.

“Although utilizing the SMB technique and avoiding the helical mode may reduce cataract risk among children likely to receive multiple examinations, it is acknowledged that clinical requirements must take priority,” the team concluded. “Further debate on the usefulness of eye inclusion for CT head examinations is encouraged.”

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